Wireless communication systems keep evolving to meet the needs for providing continuous and faster access to a data network. In order to meet these needs, wireless communication systems may use multiple carriers for the transmission of data. A wireless communication system that uses multiple carriers for the transmission of data may be referred to as a multi-carrier system. The use of multiple carriers is expanding in both cellular and non-cellular wireless systems.
A multi-carrier system may increase the bandwidth available in a wireless communication system. For instance, a dual carrier system may double the bandwidth when compared to a single carrier system and a tri-carrier system may triple the bandwidth when compared to a single carrier system, etc. In addition to this throughput gain, diversity and joint scheduling gains may also be achieved. This may result in improving the quality of service (QoS) for end users. Further, the use of multiple carriers may be used in combination with multiple-input multiple-output (MIMO).
By way of example, in the context of Third Generation Partnership Project (3GPP) system, dual cell high speed downlink packet access (DC-HSDPA) is included in Release 8 of the 3GPP specifications. With DC-HSDPA, a base station (also referred to as a Node-B) communicates with a wireless transmit/receive unit (WTRU) over two downlink carriers simultaneously. This may double the bandwidth and the peak data rate available to WTRUs and also has a potential to increase the network efficiency by means of fast scheduling and fast channel feedback over two carriers.
For DC-HSDPA operation, each WTRU may be assigned two downlink carriers: an anchor carrier (primary carrier) and a supplementary carrier (secondary carrier). The anchor carrier may carry dedicated and shared control channels used for high speed downlink shared channel (HS-DSCH), enhanced dedicated channel (E-DCH), and dedicated channel (DCH) operations (e.g., fractional dedicated physical channel (F-DPCH), E-DCH HARQ indicator channel (E-HICH), E-DCH relative grant channel (E-RGCH), E-DCH absolute grant channel (E-AGCH), common pilot channel (CPICH), high speed shared control channel (HS-SCCH), and high speed physical downlink shared channel (HS-PDSCH), and the like). The supplementary carrier may carry the CPICH, HS-SCCH and HS-PDSCH for the WTRU. The uplink transmission remains on a single carrier as in the current systems. The high speed dedicated physical control channel (HS-DPCCH) feedback information may be provided on the uplink carrier to the Node-B and contains information for each downlink carrier.
FIG. 1 shows a medium access control (MAC) layer structure for DC-HSDPA operation. The MAC-ehs entity includes one hybrid automatic repeat request (HARQ) entity per HS-DSCH transport channel. HARQ retransmissions may occur over the same transport channel and thus may reduce the benefit of frequency diversity potentially brought by the use of more than one carrier if each HS-DSCH transport channel has a fixed mapping to physical channel resources. However, it has been suggested that the mapping between an HS-DSCH and physical resources (e.g., codes and carrier frequencies) may be dynamically modified in order to provide a diversity benefit.
Multi-carrier or multi-cell uplink transmissions may be implemented in order to increase data rates and capacity in the uplink. For example, the use of multi-cell uplink transmissions may improve data processing and power consumption of the WTRU. However, because multiple uplink carriers are continuously transmitting on the uplink, even during the periods of inactivity, WTRU battery life may significantly decrease. Additionally, continuous DPCCH transmission on any secondary uplink carrier(s) may have a negative impact on system capacity.
While continuous packet connectivity (CPC) operations are implemented for single carrier uplink transmissions that help the WTRU decrease power consumption while in CELL_DCH, methods and apparatus for power control for multi-carrier uplink communications are desired.